The U.S.A. spends over $70 billion on lighting annually. LEDs can significantly reduce both the economic and environmental costs of lighting energy thereby reducing the need to import energy from foreign sources and energy-related emissions, including greenhouse gases, while improving energy efficiency in all economic sectors. Continued strong growth is expected in the LED lighting market, especially with the commercial availability of high-brightness LEDs (HB-LEDs) for LCD TVs, signals/signs, automotive, street/parking lighting, and general commercial/industrial illumination.
Considerable research and development efforts have focused on improving HB-LEDs efficiency at the LED chip level. But overall luminosity of HB-LEDs is also influenced by the process of packaging (molding/encapsulating) of LEDs. Less effort has been made to increase overall luminous efficiency of HB-LEDs, which affects LED performance as terminal products in practical applications.
Currently, silicone resin is used as a chip encapsulant for HB-LEDs. Prior to molding the LED package, the mold is lined with a flexible, unpatterned, sacrificial release film (such as made from, but not limited to, fluoropolymer ETFE), to protect both the mold and the LED package from damage when the two are separated at the end of the process. Next, a silicone resin liquid is injected into the mold to form the final product (an encapsulated LED). Under a partial vacuum, an LED chip is then pressed into the silicone resin liquid spreading the liquid throughout the molding cavity along with the release film. Once the silicone solidifies under high temperature, the final molded LED package is released from the cavity. But the silicone traps a significant amount of the light generated by the LED chip because of its high refractive index and total internal reflection (TIR). The trapped light reduces the LED package's optical efficiency as well as its overall life because of the excess heat generated by the undesirably trapped light.